Automatic compensation for electric power steering hysteresis

Abstract

A method and apparatus for improving the return-to-center motion of a steering wheel ( 16 ) wherein a determination of a first and a second value; secondly, derive a set of two values from the first value; thirdly, compute a third value from the set of two values and the first value according to a predetermined formula; and fourth, calculate a steering command using the third value and the second value for enhancing the return-to-center motion.

What is claimed is:  
     
       1. A method for enhancing a return-to-center motion of a steering wheel, the method comprising: 
       determining a hysteresis value for a steering wheel torque as a function of the steering wheel torque and position values; and  
       responsive to said hysteresis value, generating a steering command signal, said steering command signal thereby enhancing the return-to-center motion of the steering wheel;  
       wherein a magnitude of said steering command signal increases as said hysteresis value increases.  
     
     
       2. The method of  claim 1 , wherein said hysteresis value is further determined by: 
       storing a first group of input torque values and a first group of corresponding input position values when the steering wheel is turned in a first direction, said first group of corresponding input position values being determined with respect to a reference position; and  
       storing a second group of input torque values and a second group of corresponding input position values when the steering wheel is turned in a second direction, said second group of corresponding input position values also being determined with respect to said reference position.  
     
     
       3. The method of  claim 2 , wherein said hysteresis value is further determined by: 
       determining, from said first group of input torque values, a first specific torque value at which the corresponding input position value thereto is equal to said reference position; and  
       determining, from said second group of input torque values, a second specific torque value at which the corresponding input position value thereto is equal to said reference position;  
       wherein said hysteresis value is the difference between said first specific torque value and said second specific torque value.  
     
     
       4. The method of  claim 3 , wherein a given torque input is stored only if a magnitude of the corresponding input position value thereto is less than or equal to a predetermined limit. 
     
     
       5. The method of  claim 2 , wherein said first group of input torque values, said first group of corresponding input position values, said second group of input torque values, and said second group of corresponding input values are determined from outputs of sensors. 
     
     
       6. A steering system, comprising: 
       a steering wheel;  
       a steering shaft coupled to the steering wheel;  
       a set of sensors sensing a set of outputs from the steering shaft; and  
       a controller controlling a motor for assisting a vehicle operator in operating the steering system, said controller further providing an enhanced return-to-center motion of the steering wheel, wherein said controller further comprises:  
       means for determining a hysteresis value for a steering wheel torque as a function of the steering wheel torque and position values; and  
       responsive to said hysteresis value, means for generating a steering command signal, said steering command signal thereby enhancing the return-to-center motion of the steering wheel;  
       wherein a magnitude of said steering command signal increases as said hysteresis value increases.  
     
     
       7. The steering system of  claim 6 , wherein said hysteresis value is further determined by: 
       storing a first group of input torque values and a first group of corresponding input position values when the steering wheel is turned in a first direction, said first group of corresponding input position values being determined with respect to a reference position; and  
       storing a second group of input torque values and a second group of corresponding input position values when the steering wheel is turned in a second direction, said second group of corresponding input position values also being determined with respect to said reference position.  
     
     
       8. The steering system of  claim 7 , wherein said hysteresis value is further determined by: 
       determining, from said first group of input torque values, a first specific torque value at which the corresponding input position value thereto is equal to said reference position; and  
       determining, from said second group of input torque values, a second specific torque value at which the corresponding input position value thereto is equal to said reference position;  
       wherein said hysteresis value is the difference between said first specific torque value and said second specific torque value.  
     
     
       9. The steering system of  claim 8 , wherein a given torque input is stored only if a magnitude of the corresponding input position value thereto is less than or equal to a predetermined limit. 
     
     
       10. The steering system of  claim 7 , wherein said first group of input torque values, said first group of corresponding input position-values, said second group of input torque values, and said second group of corresponding input values are determined from said set of outputs from said set of sensors.